As vehicles all over the world slowly get more fuel-efficient, the energy required to make them--and their thousands of parts--is coming to represent a higher proportion of their lifetime energy footprint.

And this, in turn, is leading carmakers to focus on cutting the energy required to manufacture new cars wherever possible.

A recent study by Volkswagen looked at the carbon footprint for the most fuel-efficient model of its new Golf hatchback, known as the VW Golf TDI BlueMotion.

That vehicle, with a 103-hp (77-kilowatt) 1.6-liter turbodiesel four-cylinder engine, is rated on the European test cycle at 74 miles per gallon (3.2 liters/100 km)--although it should be noted that the European cycle customarily produces ratings 20 percent more optimistic than U.S. EPA cycles.

Volkswagen estimates that 68 percent of the car's lifetime carbon footprint is due to the diesel fuel it burns, with another 9 percent for the extraction, refining, and transportation of that fuel.

And, the company says, the carbon footprint of manufacturing the car and its parts is 22 percent of the total. (One percent is required for end-of-life recycling, VW adds.)

In 2000, just 6 percent

These data contrast with the figures from a 2000 report created by the MIT Energy Laboratory.

Electric cars, meanwhile, have lower lifetime carbon footprints than most gasoline and diesel fueled vehicles because they convert 80 percent or more of the electricity used to charge them into forward motion--against 25 to 40 percent for combustion-engined cars.

That means that electric cars use far less energy to move themselves around, significantly lowering their carbon footprint.

The carbon profile of that energy, however, varies greatly depending on how the electricity is generated--but electric cars remainlower-carbon than most combustion vehicles even if they are charged from relatively high-carbon electricity grids.

The Union of Concerned Scientists put out a graphic showing the gas-mileage equivalency state by state. In states like California, with relatively low-carbon grids, the fuel-economy equivalent is so high as to be unreachable even by the best hybrids or diesels.

That lower carbon number gives their makers more leeway to use exotic materials while still keeping the number lower.

The 2014 BMW i3 is the first volume production car with a body shell made of carbon-fiber-reinforced plastic (CFRP), a material that requires far more energy input than conventional stamped steel bodies.

But BMW still says that the lifetime emissions of an i3 are just two-thirds those of a diesel BMW 118d when recharged on the average European grid mix. Using entirely renewable sources to charge it cuts that to 50 percent of the lifetime carbon of that highly-efficient diesel car..

Most major regions of the world now have rules that limit the average carbon emissions from new vehicles, or require minimum levels of fuel efficiency--both of which reduce their lifetime energy usage.

But the question for the future then becomes whether future carbon emissions regulations look at a car's overall lifecycle footprint--not just at the fuel it burns.

Volkswagen provided airfare, lodging, and meals to enable High Gear Media to bring you this first-person report.